1. Field of the Invention
The present invention relates to a keypad structure. Particularly, the present invention relates to a keypad structure wherein the protrusions are disposed on the inner surface of the casing of the mobile phone.
2. Description of the Related Art
Mobile phones are popular and universal around the world. There has recently been a trend towards various colors for the appearances of the mobile phone. Conventionally, the casing of a mobile phone is manufactured in accordance with the following: A flat sheet is produced by injection molding, wherein the flat sheet has a colored pattern thereon. Then, the flat sheet is perforated by punching to obtain a casing for the mobile phone, wherein the casing is provided with holes for keypad buttons.
The casing is mounted on the mobile phone which has an elastic sheet inside. The elastic sheet includes a plurality of keypad buttons and protrusions on the bottoms of the keypad buttons. Three kinds of elastic sheets are provided by manufacturers: (1) an elastic sheet is made of rubber, wherein the keypad buttons and the protrusions are integrally formed (2) an elastic sheet is also made of rubber, but the keypad buttons and the protrusions of the elastic sheet are separately produced and then connected (3) the protrusions of the elastic sheet are made of rubber while the keypad buttons are made of different material stiffer than rubber (e.g. Taiwan Patent No. 457191). In operation, a key button of the elastic sheet is pressed so that the protrusion on the bottom of the key button pushes against a resilient metal piece on the printed circuit board of the mobile phone. When the key button is released, the protrusion on the bottom of the key button is restored via the elasticity. However, each conventional elastic sheet has problems of material fatigue after longtime operation, a limited structural design, and requires complex manufacturing processes and high manufacturing cost.